Montes de Oca Joan M, Dhanasekaran Johnson, Córdoba Andrés, Darling Seth B, de Pablo Juan J
Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States.
Advanced Materials for Energy-Water Systems (AMEWS) Energy Frontier Research Center, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, United States.
ACS Nano. 2022 Mar 22;16(3):3768-3775. doi: 10.1021/acsnano.1c07706. Epub 2022 Mar 1.
Janus, or two-sided, charged membranes offer promise as ionic current rectifiers. In such systems, pores consisting of two regions of opposite charge can be used to generate a current from a gradient in salinity. The efficiency of nanoscale Janus pores increases dramatically as their diameter becomes smaller. However, little is known about the underlying transport processes, particularly under experimentally accessible conditions. In this work, we examine the molecular basis for rectification in Janus nanopores using an applied electric field. Molecular simulations with explicit water and ions are used to examine the structure and dynamics of all molecular species in aqueous electrolyte solutions. For several macroscopic observables, the results of such simulations are consistent with experimental observations on asymmetric membranes. Our analysis reveals a number of previously unknown features, including a pronounced local reorientation of water molecules in the pores, and a segregation of ionic species that had not been anticipated by previously reported continuum analyses of Janus pores. Using these insights, a model is proposed for ionic current rectification in which electric leakage at the pore entrance controls net transport.
两面（Janus）带电膜有望成为离子电流整流器。在这类系统中，由两个电荷相反区域组成的孔可用于根据盐度梯度产生电流。随着纳米级两面孔直径变小，其效率会显著提高。然而，对于潜在的传输过程，尤其是在实验可及条件下的传输过程，人们了解甚少。在这项工作中，我们利用外加电场研究了两面纳米孔中整流的分子基础。使用含有明确水分子和离子的分子模拟来研究水性电解质溶液中所有分子物种的结构和动力学。对于几个宏观可观测量，此类模拟结果与非对称膜的实验观测结果一致。我们的分析揭示了许多此前未知的特征，包括孔内水分子明显的局部重新定向，以及离子物种的分离，这是此前对两面孔进行的连续介质分析未曾预料到的。基于这些见解，我们提出了一个离子电流整流模型，其中孔入口处的漏电控制着净传输。
